1. Field of the Invention
The present invention generally relates to a lens, and more particular, to a zoom lens.
2. Description of Related Art
Usually, a zoom lens is composed of two lens groups, wherein the first lens group near an object side has a negative refractive power for diverging light beams, while the second lens group has a positive refractive power for converging light beams.
However, a conventional zoom lens is composed of two lens groups and having five or six lenses. The conventional zoom lens has an f-number greater than 3.5, so an aperture of the conventional zoom lens is respectively smaller. For example, the conventional zoom lenses disclosed by U.S. Pat. Nos. 6,324,014 and 5,541,772 have the above-mentioned disadvantage and are hard to reach a large relative aperture. In addition, such kinds of conventional zoom lenses employ an aspherical lens for eliminating the aberration, which is more expensive and leads to higher production cost. Furthermore, for the above-mentioned conventional zoom lens to reach a larger relative aperture, more lenses incorporated with the required aspherical lenses are needed to eliminate the aberration, therefore, the production cost of the conventional zoom lens is further increased.